Continuous casting has long been one of the more active areas of innovation in the metallurgical field and as a result a relatively large volume of patent and other technical literature has developed and continues to grow. For a variety of reasons, however, comparatively very few of the concepts set out in the voluminous prior art have materialized in commercial form. The continuous casting systems for metal that have reached commercial status have usually involved the use of some type of mechanical contacting mold to contact, contain and shape molten metal such as copper while it is solidifying. These molds take the form of casting wheels and casting belts and may in the case of the so called "dip-forming" process take the form of seed rod which is in effect an internal mold.
As will be developed in more detail below, the present invention involves as a central feature the use of an alternating electromagnetic field to create, support and contain out of continuous contact with any containing surface upwardly moving molten metal, and eliminates the necessity for the casting wheel, the casting belt, the seed rod or other contacting molds now used in the industry. In addition to simplifying the continuous casting of metals and other commercial production systems, the process of this invention opens the opportunity of making small to moderate quantities of brass, nickel and other metallic products by continuous casting instead of by the more expensive billet casting and hot rolling processes presently in general use.
With generally the same objectives in view, others have proposed the use of an electromagnetic mold to contain a metal melt pool on top of a downwardly moving ingot while the outer lateral portions of the pool are being solidified. This general departure is described in U.S. Pat. No. 3,467,166 (Getselev, et al) and is further developed in U.S. Pat. No. 3,605,865 (Getselev); U.S. Pat. No. 3,735,799 (Karlson); U.S. Pat. No. 4,014,379 (Getselev); and U.S. Pat. No. 4,126,175 (Getselev). In each instance, accretion is longitudinal, melt being delivered semi-continuously or continuously by gravity flow on the upper end of the descending ingot. One of the more serious drawbacks of this approach is the fact that the "fail safe" characteristic of casting upwardly is absent. Thus, in the event of an unexpected electric power failure, molten metal will spill out of the downward casting apparatus instead of merely running back, as in this invention, into the holding vessel. In addition, the possibility melt overflow and breakout in downward casting require constant careful control of both the melt feed rate and the ingot removal rate. Moreover, these rates are drastically limited by a heat exchange problem which consequently diminishes the commercial potential of this special type of continuous casting.
According to another recent departure described in U.S. Pat. Nos. 3,746,077 (Lohikoski, et al) and 3,872,913 (Lohikoski) assigned to Outokumpo Oy, molten metal being either hydrostatically forced or pulled by vacuum upwardly into an open-ended, vertically-disposed mechanical mold as freshly-formed and cooled cast product is discontinuously and intermittently removed from physical contact with the upper end of the mechanical mold which contains the molten metal. In this way, the fail-saft feature is gained but only by accepting the major shortcomings of the external contact mold and the extraction mechanisms associated with its use.